The present invention relates generally to a mechanical interlock apparatus for two or more circuit breakers. More particularly, the invention relates to an improved mechanical interlock for two or more switch-type circuit breakers that reduces the amount of space required to operate the mechanical interlock, while still providing easy access for replacement of individual circuit breakers and preventing dismantling using ordinary hand tools.
It is common to restrict the movement, and thereby prevent the unintended operation, of switch-type circuit breakers. It is particularly desirable to prevent the unintended operation of a switch-type circuit breaker when more than one power source is available to provide electrical service. For example, secondary power sources, such as emergency or back-up generators, are commonly employed to maintain LifeLine Support (e.g., 911 emergency telephone service) in the event that the primary power source, typically commercial utility power, is interrupted. If the primary and secondary power sources are not prevented from being energized at the same time, referred to herein as xe2x80x9cinterlocked,xe2x80x9d electrical power can flow unexpectedly and cause damage to equipment or serious injury to personnel. A circuit breaker interlock apparatus is utilized to ensure that no more than one power source energizes the electrical system at the same time. Although electrically activated circuit breaker interlocks may be utilized to automatically isolate multiple power sources, there are situations when a mechanically activated interlock is preferred. A mechanically activated circuit breaker interlock, referred to herein as a xe2x80x9ccircuit breaker mechanical interlock,xe2x80x9d is typically less costly to install and maintain, and is equally reliable as long as there are service personnel present to operate the mechanical interlock.
Known circuit breaker mechanical interlock apparatus isolate one or more circuit breakers and thereby prevent more than one power source from energizing an electrical system at the same time. In particular, known mechanical interlock apparatus prevent more than one switch-type circuit breaker from being operated at any given time. An example of such a circuit breaker mechanical interlock apparatus is shown and described in U.S. Pat. No. 6,069,328, which is assigned to the assignee of the present invention. The circuit breaker mechanical interlock apparatus includes a housing that defines a receptacle for receiving two or more switch-type circuit breakers mounted in parallel, linear alignment and an interlock plate positioned adjacent the switches of the circuit breakers. The interlock plate has an opening that is sized to provide access to only one of the switches at a time. The interlock plate is moveable on the housing relative to the circuit breakers between a first position wherein one of the switches of the switch-type circuit breakers is accessible through the opening, but the remaining switches are not, and a second position wherein a different one of the switches of the switch-type circuit breakers is accessible through the opening, but the remaining switches are not.
The interlock plate shown and described in U.S. Pat. No. 6,069,328 cannot be moved from the first position to the second position unless all of the switches are in an xe2x80x9cOFFxe2x80x9d or xe2x80x9cNEUTRALxe2x80x9d position such that the electrical system is not energized. Once the interlock plate is moved from the first position to the second position, the switch that is accessible through the opening in the second position may then be moved to the xe2x80x9cONxe2x80x9d position. However, as illustrated by the phantom lines in FIG. 2 of the U.S. Pat. No. 6,069,328 , the interlock plate extends substantially beyond the perimeter of the housing when the interlock plate is positioned to access the left-most circuit breaker. Obviously, the interlock plate will extend substantially beyond the perimeter of the housing when the interlock plate is similarly positioned to access the right-most circuit breaker. As a result, a lateral space greater than the width defined by the perimeter of the housing is required to operate the circuit breaker mechanical interlock. Of course, the width of the housing could simply be increased to accommodate the lateral movement of the interlock plate. Alternatively, the circuit breakers could be mounted vertically to conserve lateral space. However, the increased width of the housing (or the increased height of the housing if the circuit breakers are arranged vertically) would likewise interfere with the operation and/or placement of other components of the electrical power system whenever dense packaging is required. Thus, while the apparatus of the U.S. Pat. No. 6,069,038 is suitable for use in many instances, there are situations in which there is insufficient space available adjacent the housing to operate such a circuit breaker mechanical interlock. Accordingly, a circuit breaker mechanical interlock apparatus is needed that reduces the amount of space required to operate the mechanical interlock, without unnecessarily increasing the overall width of the apparatus.